This application relates generally to an abradable seal for use in a gas turbine engine to protect tips of compressor blades.
Gas turbine engines include compressor rotors including a plurality of rotating compressor blades. Minimizing the leakage of air between tips of the compressor blades and a casing of the gas turbine engine increases the efficiency of the gas turbine engine as the leakage of air over the tips of the compressor blades can cause aerodynamic efficiency losses. To minimize this, the gap at tips of the compressor blades is set so small that at certain conditions, the blade tips may rub against and engage an abradable seal on the casing of the gas turbine. The abradability of the seal material prevents damage to the blades while the seal material itself wears to generate an optimized mating surface and thus reduce the leakage of air.
Prior abradable seals have been made of a mixture of materials that produce an abradable seal having large pores. For example, the pores can have a size of 400 to 1800 microns. The large pores can cause leakage of air flow from the high pressure side of the tips of the compressor blades to the low pressure side, which can result in aerodynamic efficiency losses and an acoustic damping effect. Aerodynamic efficiency losses can also be caused by pressure fluctuations associated with air that flows into and out of the large pores of the abradable seal.
One prior abradable seal is formed of felt metal and includes large pores. However, this abradable seal can cause a 1% reduction in efficiency over an abradable seal with a hard smooth surface. Another prior abradable seal has filled porosity to increase efficiency. However, the hard and dense material of the seal requires that the tips of the compressor blades be tipped with hard or abrasive materials to improve the ability of the compressor blades to cut the seal material.